using INDEX or not with same WHERE clause

Hello group

I'm Working on Oracle parallel Server (2 nodes) 8.1.7.

I've got a big table (>500 000 rows)

I'm using EXPLAIN PLAN and plan_table to understand how CBO execute my query. I've done an "analyze table tlogs estimate statistics" before.

Here is my query : select count(*) from tlogs where column1='A VALUE';

This give me the result '9' in six second.

and when i do a

select column2 from tlogs where column1='A VALUE';

This give me the nine rows in more than 2 minutes.

Explain PLAN tell me that in the first query, the index on column1 is used, and in the second case, the index on column1 is NOT use and there is a full table scan.

I don't understand why Oracle choosing an FTS in the second case (with the same WHERE condition)

Thanks for your help. Received on Wed Dec 12 2001 - 09:08:39 CST